A color image sensor for a digital camera or other device normally contains a color filter array (CFA) or color filter mosaic (CFM) that overlies an array of light sensors. FIG. 1, for example, illustrates a conventional color image sensor 100 including a sensor array 110 with an overlying CFA 120. Sensor array 110 can be an integrated semiconductor device such as a charge-coupled device (CCD) sensor array or a complementary metal-oxide-semiconductor (CMOS) image sensor. CFA 120 in the example of FIG. 1 is a Bayer or GRGB filter, which is a rectangular array of green, red, and blue color filters arranged such that each color filter that is not on the edge of CFA 120 is surrounded by four green filters, two red filters, and two blue filters. Pixel sensors 112 under respective color filters of CFA 120 can integrate the energy of light transmitted through the respective color filters to measure the intensities of incident green, red, or blue light. Each of these measurements indicates a color component (e.g., green, red, or blue level) of a pixel corresponding to that pixel sensor 112. A process commonly referred to as demosaicing can then determine other color components of pixels through interpolations using the color components measured by neighboring pixel sensors.
CFAs such as CFA 120 can be manufactured on sensor arrays using integrated circuit fabrication techniques to fabricate each color-specific optical filter. Such optical filters come in different types. The most common optical filters are absorptive filters and reflective filters. Absorptive optical filters absorb the undesired wavelengths of light so that only the wavelength or wavelengths of interest are transmitted through the filter. Thus, absorptive optical filters must be thick enough (e.g., at least several wavelengths thick) to allow efficient absorption of the undesired wavelengths. In contrast, reflective optical filters reflect undesired wavelengths of light. Reflective optical filters can be made using thin film dielectric layers stacks, which provide accurate control over the filter central frequency and spectral width. Fabrication of reflective optical filters can be quite expensive and generally requires tight control of the film thicknesses. Simpler thin structures and fabrication processes for color image sensors would be desirable.